Sugar Processing from Sugar Cane and The Derivative’s Products

Sugar cane is a member of the grass family. Sugar cane has its 'modern' origins in Papua New Guinea, and is now grown in tropical regions throughout the world. Sugar cane requires strong sunlight and abundant water for satisfactory growth. Sugar Cane farmers, usually cultivate hybrids of several species, and some varieties can grow up to five metres tall.

Sugar Cane looks rather like bamboo cane, and it is within the cane that the sucrose is stored. In the right climate Sugar Cane will grow in 12 months and, when cut, Sugar Cane will re-grow in another 12 months, provided the roots are undisturbed. Sugar is made by some plants to store the energy which they do not need straight away, rather like the way in which animals make and store fat.
The process whereby plants make sugars is photosynthesis. The plant takes in carbon dioxide from the air though pores in its leaves and absorbs water through its roots. These are combined to make sugar using energy from the sun and with the help of a substance called chlorophyll. Chlorophyll is green which allows it to absorb the sun's energy more readily and which, gives the plants' leaves their green colour. Oxygen is given off during the process of photosynthesis.
It takes between 12 months and 2 years to plant and harvest a Sugar Cane crop and some types of Sugar Cane can grow nearly as tall as a house, but this delicious food is best known as the white grains found in a bowl on nearly every dining table in the world and used to sweeten nearly everything that we eat.

1. Production Process
1.1 Extraction of Juice

Extraction of juice from sugar beet

On delivery by lorry or train, the sugar beets are cleaned in a beet washer (2). An elevator then takes the beets to slicers (3) with rotating knives where they are cut into small slices (cossettes). The sugar cannot be extracted from these slices until their cell walls have been made permeable by heat (75°C). For this purpose the cossettes are led through a mixer (4) (stirrer) where a heat exchange takes place with hot raw juice coming in the opposite direction from the diffusion towers (5). At the end of the mixing zone, the mixture of juice and slices is pumped into the diffusion towers, i.e. around 20-m-high cylinders with diameters of 4 to 8 m arranged one behind the other. Hot water, again in counter-current, is used to extract the sugar from the cossettes. The pulp is dried in drums, pelletised and used as fodder.

Extraction of Juice From Sugar Cane

The sugar cane is unloaded in bundles onto the feed table by a crane and then transported to the mills on a chain conveyor, which has sets of individual rotating knives to cut the cane into small chips. These chips then pass through mills consisting of three interlocking, fluted rollers where the juice is extracted. The mills are driven by the speed-reducing gears of steam turbines. The sugar still contained in the cane is extracted with water, the leached cane fibres leaving the last mill as bagasse, which serves as fuel for generating the process steam.

1.2 Juice Clarification
The raw juice extracted from sugar beet or sugar cane is pumped into an intermediate tank (7) and mixed with lime milk to separate any nonsugar substances contained in the raw juice. Then the raw juice is fed into a carbonatation tank (9). Carbon dioxide is added to convert the
lime into calcium carbonate, which encloses the non-sugar particles in such a manner that they may be sieved off in thickening and pressure filters (10). The compound thus extracted (11) is used as a fertiliser. The filtrate is a clear, light yellow sugar juice.

1.3 Juice Thickening (Evaporation)
After purification and filtration, the thin juice has a sugar content of 12 to 14% and must be thickened by evaporating the excess water to produce a concentrate with a sugar content of 65 to 70% (syrup). This is done in a multi-stage evaporator unit, at the end of which the juice has the desired concentration.
Evaporation is performed in two stages: initially in an evaporator station to concentrate the juice and then in vacuum pans to crystallize the sugar. The clarified juice is passed through heat exchangers to preheat the juice and then to the evaporator stations. Evaporator stations consist of a series of evaporators, termed multiple-effect evaporators; typically a series of five evaporators. Steam from large boilers is used to heat the first evaporator, and the steam from the water evaporated in the first evaporator is used to heat the second evaporator. This heat transfer process continues through the five evaporators and as the temperature decreases (due to heat loss) from evaporator to evaporator, the pressure inside each evaporator also decreases which allows the juice to boil at the lower temperatures in the subsequent evaporator. Some steam is released from the first three evaporators, and this steam is used in various process heaters in the plant.


1.4 Crystallization
The syrup from the evaporator unit is filtered (13) and fed into steamheated pans (14) where the crystallisation process is continued until crystals are formed. This is done under vacuum and at a low temperature (70 to 75°C) in order to avoid decomposition (colouring) of the sugar. As soon as the crystals have reached their proper size, the massecuite is discharged into open containers with stirring devices (15) for cooling down and further crystallisation.

1.5 Centrifuging
In the next step the viscous syrup is separated from the sugar crystals in centrifuges (16). Whereas the sugar crystals remain in the screening drum, the syrup is centrifuged through the holes of the drum and retained by the container wall. The white sugar so obtained is dried in heated drums (17) and stored in large silos (18). By dissolving, purifying, filtering and further
crystallisation, refined sugar is obtained, which is much purer than white sugar and thus of higher quality. The separated syrup undergoes two further crystallisation processes (raw sugar, afterproduct). From the runoff syrup, called molasses, no further sugar can be crystallised. It is used in the food industry, for manufacturing yeast and alcohol, and as fodder after being added to beet pulp.

Flow Chart of Sugar Process Factory


Losses and loss prevention

The following circumstances are characteristic of the losses occurring in
sugar factories:

– Heavy load on all technical facilities during the campaign
– Sometimes inadequate maintenance during the standstill period

Adequate maintenance of the plant during the standstill period is of particular
importance. Steam generators, turbines, generators, transformers,
electric motors and gears must be carefully checked during that
time and, if necessary, overhauled and preserved. Only in this way can
dangerous changes or emerging damage be recognised early enough to
be remedied.


Utilities

The piping of steam generators is often damaged due to

– lack of water following a failure of feed water pumps or measuring
and control systems;
– inadequate water treatment (boiler scale, sludge deposits);
– sugar penetrating into the boiler feed water.

Steam turbines are above all exposed to shaft failures, blade damage,
interruptions in the oil supply, overspeed due to a failure of the control
and trip devices. The drive turbines of sugar cane mills must in addition
withstand thrusts and starts under full load, leading to blade damage,
damage to bearings and broken shafts.

Damage to gears, in particular to the reducing gears of sugar cane mills,
is caused by load thrusts, starting under full load, inadequate lubrication,
entry of foreign particles and misalignments due to faulty setting,
resulting in broken teeth, pitting, broken shafts and damage to bearings.